In recent years, as a result of storage capacity expansion, processing speed increase, and device volume reduction of optical communication systems, technology of implementing a photonic-based electronic circuit portion and optical circuit portion in one chip is gradually getting more and more attentions.
Specifically, an optical coupling device is implemented and optically coupled with an external element using a grating coupler or a side coupler formed on a silicon photonics chip. The optical coupling device is coupled between a planar optical waveguide on the silicon photonic chip and an optical fiber. The method of coupling the optical fiber and the optical waveguide on the silicon photonic chip could be generally classified into two kinds, side coupling and grating coupling. The side coupling implemented through a side coupler formed on the silicon photonics chip works independently of the wavelength. However, the side coupler has a very small optical alignment tolerance between the silicon photonic chip and the optical fiber.
On the other hand, the grating coupling is the method of directly coupling the light (or optical signal) into the optical waveguide through the gratings. The grating coupler has larger optical alignment tolerance; however, it is sensitive to the wavelength. Otherwise, in the current silicon photonic chip packaging design, through the coupling between the gratings and the optical waveguide could increase the alignment tolerance. Nevertheless, owing to the approximately perpendicular angle, about 10 degrees to 20 degrees, between the gratings and optical waveguide, there might the concerns in the difficulties of processing the optical alignments between the gratings on the silicon photonic chip and optical waveguide.